In the past 20-30 years, increased interest on the part of biostatisticians and medical investigators has been exhibited in clinical trial research. In the mid-1940's, the Veterans Administration Hospital system was recognized as an ideal environment for the conduct of multicenter clinical trials, with the initiation of a study to determine the effectiveness of chemotherapy in the treatment of tuberculosis, in a joint effort with the United States Armed Forces. This research effort later evolved into what is presently known as the Cooperative Studies Program of the Medical Research Service. Within the past seven years, this program has undergone considerable growth and reorganization. This paper describes a system for the review, operation, and conduct of multicenter clinical research in a wide variety of medical specialty areas. In particular, it stresses the importance of core biostatistical coordinating centres where biostatisticians and other key support personnel constitute an integral part of the planning and development, implementation, conduct, and reporting of many cooperative studies in diverse disciplines. The paper also describes the interaction of various review bodies and a check and balance system to promote sound management and opportunity for the exchange of clinical and biostatistical methodology in the cooperative study setting.